swr: [rasterizer] Include cmath for std::isnan and std::isinf.

swr: [rasterizer] Include cmath for std::isnan and std::isinf.

This patch fixes this build error.

  CXX      rasterizer/memory/libswrAVX_la-ClearTile.lo
In file included from rasterizer/memory/ClearTile.cpp:34:0:
./rasterizer/memory/Convert.h: In function ‘uint16_t Convert32To16Float(float)’:
./rasterizer/memory/Convert.h:170:9: error: ‘__builtin_isnan’ is not a member of ‘std’
     if (std::isnan(val))
         ^
./rasterizer/memory/Convert.h:170:9: note: suggested alternative:
<built-in>: note:   ‘__builtin_isnan’
./rasterizer/memory/Convert.h:176:14: error: ‘__builtin_isinf_sign’ is not a member of ‘std’
     else if (std::isinf(val))
              ^
./rasterizer/memory/Convert.h:176:14: note: suggested alternative:
<built-in>: note:   ‘__builtin_isinf_sign’

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95180
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Tim Rowley <timothy.o.rowley@intel.com>